Chromium plating is an electrochemical process well-known in the art. There are two general types of chromium plating, hard chromium plating and decorative chromium plating. Hard chromium plating includes application of a heavy coating of chromium onto steel items typically to prevent wear, and exists in thicknesses in the thousandths of an inch (10–1000 μm). Decorative chromium plating applies a much thinner layer of chromium, in millionths of inch (0.25–1.0 μm), providing an extremely thin but hard coating for aesthetic purposes to achieve a shiny, reflective surface and protect against tarnish, corrosion and scratching of the metal beneath.
Chromium plating typical employs hexavalent chromium (chromium VI) a highly toxic material and suspected carcinogen. Use of hexavalent chromium produces hazardous sludge and requires use of expensive chemicals to reduce the waste to a nonhazardous form. Hexavalent chromium also poses an environmental risk as it may escape through spill and leaks and a health risk to individuals working with the material as hexavalent chromium solution is carried by hydrogen gas mist which is generated through the plating process, particular when performing hard chromium plating. As use of hexavalent chromium is problematic for several reasons, trivalent chromium is a desirable alternative with lower waste treatment and air scrubbing costs.
While use of trivalent chromium coatings has become a popular alternative for thin, decorative plating, problems still remain. Trivalent chromium solutions are unstable. Trivalent chromium may be oxidized to hexavalent chromium at the anode which results in an inhibition of the cathode process. Often, anode and cathode must be separated to avoid this problem but in turn this reduces practical use of this method of chrome plating. Trivalent chromium plating is problematic as neutral salts tend to build up in the plating solution and reduce efficiency. These difficulties limit the use of trivalent chromium plating to thin coating applications. While pulse current plating has been employed to obtain thicker layers, it does not produce the desired corrosion-resistant coating.
There remains a need to improve the effectiveness of trivalent chromium plating and to achieve thicker coatings so that it may be employed in wear applications to achieve functional, hard chromium plating, as well as efficient decorative chromium plating.